An HDMI cable that connects an HDMI transmission device and an HDMI reception device includes a TMDS video transmission line that transmits a video signal and a clock signal, a DDC signal line that transmits EDID information of the HDMI reception device to the HDMI transmission device, a power supply line that supplies +5V power from the HDMI transmission device to the HDMI reception device, and an HPD signal line used for connection detection (so-called hot plug detection) of the HDMI reception device to the HDMI transmission device.
The HPD signal line is typically connected to the power supply line via a resistor on a side of the HDMI reception device connected to the HDMI transmission device. Accordingly, a predetermined voltage is applied to the HPD signal line, so that a connection of the HDMI reception device is detected by the HDMI transmission device based on the voltage of the HPD signal line. In the hot plug detection, the connection of the HDMI reception device is detected regardless of whether the HDMI reception device is in an ON state.
The TMDS video transmission line transmits a video signal or the like based on a voltage change corresponding to ON/OFF control of a current on the HDMI transmission device side, on a termination condition that is pulled up to +3.3V on the HDMI reception device side in the ON state. When the HDMI reception device is in an OFF state and the TMDS video transmission line is not pulled up, a voltage of the TMDS video transmission line does not change appropriately. Therefore, the HDMI transmission device monitors the voltage change of the TMDS video transmission line, and stops the transmission of a video signal or the like when the voltage of the TMDS video transmission line does not change appropriately. In other words, it can be said that the TMDS video transmission line is used for device connection detection of the HDMI reception device, Which includes detection of an operating state (ON state or OFF state) of the HDMI reception device.
There has been known an HDMI optical cable in which the TMDS video transmission line is configured by an optical fiber wire instead of an electric wire (see, for example, Patent Document 1).